An organic light-emitting device is an electronic device which has a thin film containing a fluorescent organic compound or a phosphorescent organic compound interposed between an anode and a cathode. In the device, holes and electrons are injected from the respective electrodes to yield excitons of the fluorescent compound or the phosphorescent compound and then light is generated from the organic light-emitting device when the excitons return to their ground state.
Recently, a significant progress has been made relating to an organic light-emitting device. The characteristic feature includes that high luminance, a variety of emission wavelengths and a high-speed response can be obtained at a low voltage and also a thin and light-weight light-emitting device can be produced. For these reason, application of an organic light-emitting device in a broad and diverse range has been suggested.
At a practical level, however, more improved luminance or higher conversion efficiency is required. In addition, there are still a lot of problems associated with durability, for example, degradation due to use for a long period of time or due to atmosphere including oxygen, moisture or the like.
Furthermore, for an application in a full-color display and the like, light emission of red, green, and blue colors with good color purity is required, but it cannot be said that such needs are completely met at the present moment.
To solve the above described problems, a dibenzo[c,g]fluorene compound has been proposed as a constitutional material for an organic light-emitting device. For example, International Publication WO2003/051092, U.S. Patent Application Publication No. 2004/0131880, and Wei-Zhi Wang et. al., “Synthesis, photophysics, and electroluminescence of poly(dibenzo fluorene)s”, Macromolecular Rapid Communications Vol. 27, No. 14, p. 1142 (2006), can be mentioned in which a dibenzo[c,g]fluorene compound or an organic light-emitting device using a dibenzo[c,g]fluorene compound as a constitutional material is described.
The dibenzo[c,g]fluorene compound disclosed in International Publication WO2003/051092 is substituted at 5-position and 9-position with a heterocyclic group with hole transporting property such as an oxadiazole group, a thiadiazole group, a triazole group, a diarylamine group, and a carbazole group.
In addition, the dibenzo[c,g]fluorene compound disclosed in U.S. Patent Application Publication No. 2004/0131880 is also substituted at 5-position and 9-position with a heterocyclic group such as a thiophene group, and a carbazole group.
Incidentally, according to the literature by Wei-Zhi Wang et. al. (“Synthesis, photophysics, and electroluminescence of poly(dibenzo fluorene)s”, Macromolecular Rapid Communications. Vol. 27, No. 14, p. 1142 (2006)), the characteristics of an organic light-emitting device in which a polymer having a dibenzo[c,g]fluorene skeleton is used as a constitutional material are described. However, it cannot be said that the characteristics exhibited as a polymer material are necessarily reflected as they are on a low molecular weight material. That is because, as having a molecular weight distribution contrary to a low molecular weight material, the polymer material is a mixture containing many compounds having various molecular weights and at the same time is a material which has an energy distribution with a certain range. Therefore, for example, the light-emitting behavior of a polymer material is basically different from the light-emitting behavior of a low molecular weight material.